Field of the Invention
The present invention relates as general to pumps and particularly pertains to a new and useful valveless pump for delivering liquid or gaseous media.
A valveless pump described in U.S. Pat. No. 4,405,294 dated Sept. 20, 1983, has two pistons which are guided jointly in the bore of a cylinder. The two pistons are moved in the same direction, such that one of the pistons regularly performs the full lifting or pumping movement, while the other piston performs only part of the lift. The difference in lifts forms, together with the cross section of the cylinder bore, the delivery volume of the pump.
One of the pistons is attached without axial clearance to a slide, which surrounds the cylinder in the shape of a U, while the other piston is not attached to the slide, as a result of which an axial lift relative to the slide is possible. This piston acts as a pump piston.
When the slide is moved to and from in its longitudinal direction by a drive, the pump piston lags behind the movement of the slide and consequently lags behind the movement of the control piston connected to it due to the friction effect of a braking spring that touches it on both sides. One end face of it lies in one of the directions of movement of the end face of the control piston, while a hollow space, which represents the delivery volume, is formed in the other direction of movement. The empty space or cavity is constantly forming and disappearing in the cylinder at the dead centers of the movement. The inlet and outlet pipes for the medium to be delivered are located at the cavity of the cylinder.
If the pump is to deliver at high back pressure, the braking spring must be very strong. However, this leads to great wear on the spring and the piston.
This disadvantage is avoided with the pump described in U.S. Pat. No. 3,302,578. Here, the braking force is consumed by an electromagnet. The latter is energized and de-energized by limit switches during the pump cycle, so that the braking force is present only during the ejection phase, during which the medium to be pumped is delivered through the outlet. Movement causing friction and consequently intense wear are thus avoided. However, a disadvantage of this pump is the fact that the large mass of the electromagnet must constantly be accelerated. This requires a large and heavy design and relatively high drive power for the pump.
Both pumps described above share the disadvantage of a low discharge velocity, which is predetermined by the maximum speed of rotation of the eccentric drive used.